Many welding applications need to be performed using welding power supplies that are able to be plugged into a standard 110-120 volt AC, 60 Hz outlet, such as the type that may be found in most homes, offices, and businesses. Because of the low output voltage of the standard AC outlet, a relatively high current is needed from the outlet to melt the electrode and base material. However, the typical AC input for such an outlet may be limited to only 15 (or 30) amps by a circuit breaker, which may also serve other AC outlets as well. Accordingly, the power that may be obtained from such an AC outlet is limited, thus further limiting the power that may be provided to the weld.
Since standard AC outlets are limited to 15 (or 30) amps typically, this only allows for approximately 1800 (or 3600) watts of power for welding applications. Thus, for example, assuming a 90% efficient design and a power factor of 1, the available welding power for a 30 amp circuit at 120 volts AC would be only 3240 watts. For various welding processes, this amount of power would produce the following welding currents: Stick Welding—130 A; MIG Welding—150 A; and TIG Welding—185 A.
This power is available 100% of the time. However, many welding applications need more current. Thus, because most welding is not at 100% duty cycle, it would be helpful to use the power during the non-welding time to charge an energy storage device. Such a device could be any number of things—most commonly a battery. This stored energy alone or combined with power from the outlet can be used to produce any amount of welding power.
Some prior art AC welders provided an unbalanced output to offset the naturally occurring unbalanced load when using a tungsten electrode, while yet other types of known welding power supply use only battery power as an input. However, these types of power supplies are generally limited in the amount and in the duration of power that they can provide for welding applications.
U.S. Pat. No. 6,777,649 relates to a welding-type power supply that uses an energy storage device, such as a battery, as a voltage boost mechanism. Generally, this patent provides for welding from a standard AC duplex outlet and provides up to a 150 amp output, at an output voltage of up to about 25 volts. A battery is provided after the voltage regulation and in series with the welding output, such that the battery simply “boosts” (or adds to) the output voltage. Thus, the power circuit need only provide a 12 volt output, with an additional 12 volts coming from the battery. However, the power supply in this patent does not pull any extra current from the energy storage element, i.e., the battery is not being charged during the non-welding time.
Thus, it would be preferable to use an energy storage element that can be charged from a standard 110-120 volt AC outlet at a 15 to 30 amp rate, but will also be able to provide higher power output for short periods of time for a welding operation. By using different charging systems, the welder could be adapted to work with various input supplies, AC or DC, as well as high or low power levels. Using such a system, it would be possible to get unlimited welding current. The amount of welding current would be dependent on the size of the energy storage element.